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HOG CHOLERA TRANSMISSION THROUGH 
INFECTED PORK 



A THESIS 

Presented to the Faculty of the Graduate School 

op Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

RAYMOND RUSSELL BIRCH 



[Reprinted from the Journal of the American Veterinary Medical 
Association, Vol. LI. N. S. Vol. 4, No. 3, June, 1917.] 



HOG CHOLERA TRANSMISSION THROUGH 
INFECTED PORK 



A THESIS 

Presented to the Faculty op the Graduate School 
op Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

RAYMOND RUSSELL BIRCH 



[Reprinted from the Journal of the American Veterinary Medical 
Association, Vol. LI. N. S. Vol. 4, No. 3, June, 1917.] 



1 n 



3 






In escwmgt. 

Cornell OnU. Library 

JUN 1 9 1917 



HOG CHOLERA TRANSMISSION THROUGH IN- 
FECTED PORK* 



K. E. Birch, Ithaca, N. Y. 



There is no other acute infectious disease of animals which is 
so widespread as hog cholera. It occurs in almost, if not quite, 
all countries in which swine are raised, and in some countries there 
are few large areas entirely free from it. While it is most pre- 
valent near the more important shipping routes and in localities 
where large numbers of hogs are raised, it nevertheless appears 
frequently on remote farms and in localities far removed from 
busy traffic routes and centers. Its appearance in these seemingly 
well isolated places has been puzzling, for it is well known that it 
is caused by a specific virus, and that whenever, it appears in a 
herd, the virus has in some manner been transferred to the herd 
from other infected animals. 

Hog cholera virus, while it is not known to multiply outside 
the bodies of swine, is very tenacious and resists most natural de- 
structive influences for long periods of time. A very small quan- 
tity 1 of it will infect an animal, and it is, therefore, commonly sup- 
posed that such casual carriers as crows "buzzards, and also various 
domestic animals not themselves susceptible to hog cholera, are in 
a large measure responsible for the many seemingly mysterious 
appearances of the disease. While the facts at hand do not admit 
doubt concerning the possibility of hog cholera virus transmission 
by these carriers, there are good reasons to doubt whether they 
possess the degree of importance usually attributed to them. 
Circumstances seem to point to some important means of trans- 
mission less precarious than is furnished by such carriers. 

Hogs that are fed garbage very frequently contract cholera 
and garbage often contains pork trimmings. Since garbage feed 
ing is habitual both with farmers who feed only their own kitchen 
refuse and with men who make a business of removing and feeding 
city garbage, it seems reasonable to suppose that this practice may 



* Presented at the Meeting of the A.V.M.A. Section on Sanitary Science 
and Police, August 1916, Detroit, Mich. 



1. King places the minimum fatal dose of hog cholera virus for a 50 lb. 
pig somewhere between 1/215 and 1/300 c.c. In his experiments the doses 
were administered intramuscularly. 



be responsible for many new herd infections. Further evidence 
supporting this belief is found in the facts that marketing the 
seemingly well animals in newly infected herds is a common prac- 
tice, and that hog cholera virus appears in the blood stream of in- 
fected animals quite early in the course of the disease. 

In the past, very little importance seems to have been at- 
tached to the transmission of hog cholera through infected bits of 
pork. Dr. James Law 2 mentions pork trimmings as a possible 
source of infection, but he lays special stress on dangers incident 
to feeding slaughter house refuse. Hutyra and Marek 3 make no 
mention of market pork as a possible means of hog cholera trans- 
mission, and neither do Friedburger and Frohner 4 . Dr. M. Dorset 5 
in summarizing the various channels of inter-herd spread of the 
disease makes no mention of infected pork trimmings. So far as 
we know the first outbreak traced with any degree of accuracy to 
infected market pork was one in Canada which McGilvray G reported 
in 1912. Even that outbreak seems to have been regarded as an 
exception for very little has been done looking toward the preven- 
tion of this means of hog cholera transmission. 

Anti-hog cholera serum has removed one of the greatest ob- 
stacles in the way of hog cholera control. Not only does it pro- 
tect herds in which the disease is just starting and prevent its ap- 
pearance in other threatened herds, but it prevents, or should pre- 
vent, these herds from being shipped to market at times when they 
are in condition to infect other swine. It thus removes an almost un- 
bearable hardship to swine breeders that otherwise would accom- 
pany the enforcement of strict sanitary measures to prevent ship- 
ping cholera infected hogs. It has given good reasons to hope for 
the more complete control or eradication of hog cholera, and in so 
doing it has centered the efforts of a large number of veterinarians 
on a more thorough study of the disease itself, and on sanitary 
measures for its control. Since it cannot be effectively controlled 
as long as any one common means of transmission remains un- 
known or unheeded it has seemed desirable to procure exact ex- 
perimental data on the effects of feeding susceptible pigs bits ot 
pork such as might be found in garbage. 

The experiments have been conducted with three kinds of 
pork; fresh, refrigerated, and cured. Some of the specimens of 
each kind were taken from carcasses that would have passed in- 
spection, and others were taken from carcasses that would have 



been condemned. In all the experiments, before the specimens 
were removed for feeding, the hams were scalded and scraped as 
is done in butchering. Except as otherwise stated the material 
fed consisted of all or a part of the head of a femur together with 
adjacent parts. With one exception, experiment No. 1 in table 
No. 2, the hams all came from small shoats weighing less than one 
hundred pounds each, a fact which might have considerable in- 
fluence on results obtained from feeding cured pork. Large hams 
would naturally be expected to harbor virus in their depths with 
somewhat greater regularity than small ones when both are sub- 
jected to killing influences that work from without. 

The susceptible pigs to which the pork trimmings were fed 
were isolated with great care. In the earlier experiments small 
fly-tight pens were constructed of screen and matched lumber for 
this purpose. These were located on a hill several hundred feet 
from hog yards of any kind. When infection occurred in a pen 
it was immediately burned, and a new one was constructed on 
fresh soil for further experiments. The pigs fed in later experi- 
ments were placed in small individual fire brick pens so con- 
structed that the attendant could not touch the pigs within. Food 
and water were introduced through a joint of tile. After each 
experiment the pen used was cleaned out and a wood fire was 
kindled inside and allowed to burn for several hours. Thus, in 
all cases heat, rather than disinfectants, was used to destroy the 
virus. Most of the pigs were isolated a week or more before being 
fed and in no case did disease appear previous to feeding. In all 
cases the experimental pigs were selected from a herd of suscepti- 
ble animals, and, except as noted, disease did not appear in this 
herd subsequent to the time the animals were removed. These 
two facts practically exclude the possibility that any of the ex- 
perimental animals were infected prior to the time at which they 
were isolated. 

In judging the part played by meat inspection in removing 
cholera infected carcasses from the market, the federal meat in- 
spection regulations have been selected as a standard, because 
most of the meat inspected in this country is inspected by federal 
employees or by others who follow the federal regulations quite 
closely. Following are the paragraphs that govern antemortem 
and postmortem inspection in their relation to hog cholera: 



Regulation 9, section 2, paragraph 2. "All hogs plainly show- 
ing on ante-mortem inspection that they are affected with either 
hog cholera or swine plague shall be marked 'U. S. condemned' 
and disposed of in accordance with section 8 of this regulation." 

Regulation 9, section 2, paragraph 3. "If a hog has a tem- 
perature of 106°F. or higher and is of a lot in which there are 
symptoms of either hog cholera or swine plague, in case of doubt 
as to the cause of the high temperature, after being marked for 
identification, it may be held for a reasonable time under the su- 
pervision of an inspector, for further observation and taking of 
temperature. Any hog so held shall be reinspected on the day it 
is slaughtered. If upon such reinspection, or, when not held for 
further observation and taking of temperature, then on the ori- 
ginal inspection, the hog has a temperature of 106 °F. or higher 
it shall be condemned and disposed of in accordance with section 
8 of this regulation." 

Regulation 9, section 2, paragraph 6. "All animals which, 
on ante-mortem inspection, do not plainly show, but are suspected 
of being affected with, any disease or condition that, under these 
regulations, may cause condemnation, in whole or in part, on 
post-mortem inspection, shall be so marked as to retain their iden- 
tity as suspects until final post-mortem inspection, when the car- 
casses shall be marked and disposed of as provided elsewhere in 
these regulations, or until disposed of in accordance with section 
7 of this regulation." 

Regulation 9, section 4, paragraph 1. "All hogs, even though 
not themselves marked as suspects, which are of lots one or more 
of which have been condemned or marked as suspects under sec- 
tion 2 of this regulation for either hog cholera or swine plague, 
shall, so far as possible be slaughtered separately and apart from 
all other animals passed on ante-mortem inspection." 

Post-mortem inspection. 

Regulation 11, section 4, paragraph 1. "The carcasses of all 
hogs marked as suspects on ante-mortem inspection shall be given 
careful post-mortem inspection, and if it appears that they are 
affected with either acute hog cholera or swine plague, they shall 
be condemned." 

Regulation 11, section 4, paragraph 2. "Carcasses of hogs 
which show acute and characteristic lesions of either hog cholera 
or swine plague in any organ or tissue, other than the kidneys or 
lymph glands, shall be condemned. Inasmuch as lesions resem- 
bling lesions of hog cholera or swine plague occur in the kidneys 
and lymph glands of hogs not affected with hog cholera or swine 
plague, carcasses of hogs in the kidneys or lymph glands of which 
appear any lesions resembling lesions of hog cholera or swine 
plague shall be carefully further inspected for corroborative 
lesions. On such further inspection — 



"(a) If the carcass shows such lesions in the kidneys, or in 
the lymph glands or both, accompanied by characteristic lesions 
in some other organ or tissue, then all lesions shall be regarded as 
those of hog cholera or swine plague, and the carcass shall be con- 
demned. 

" (b) If the carcass shows in any organ or tissue, other than 
the kidneys or lymph glands, lesions of either hog cholera or swine 
plague which are slight and limited in extent, it shall be passed 
for sterilization in accordance with regulation 15. 

"(c) If the carcass shows no indication of either hog cholera 
or swine plague in any organ or tissue other than the kidneys or 
lymph glands, it shall be passed for food, unless some other pro- 
vision of these regulations requires a different disposal." 

Most of the virus used in the experiments was the same as 
was used in our routine work of serum production. It was of an 
exceedingly virulent strain obtained originally from Dr. W. B. 
iNiles of Ames, Iowa. Pigs inoculated with 2 c.c. of this virus 
were usually ready to kill for virulent blood in seven days. In 
the remainder of the experiments the virus used was obtained 
from Dr. A. D. Fitzgerald, Columbus, Ohio. This also was of a 
highly virulent strain. 

The method of securing carcasses that would pass inspection 
was to inject small shoats with 2 c.c. each of virulent blood and 
record temperatures every twenty-four hours subsequent to in- 
jections. When a decided elevation was recorded the pig was 
killed and autopsied ; then the ham was removed and scalded and 
a specimen secured for feeding. In each case the virus was in- 
jected into the right ham and the specimen fed was secured from 
the left ham. Complete data concerning these animals appears 
in table No. 1. Relative to the interpretation of results it should 
be stated that, except as noted, all the lesions produced were of 
the acute form of hog cholera, and all the animals that sickened 
displayed symptoms similar to those produced by that disease. 
The term "typical lesions of cholera" as used in all the tables in- 
dicates that the animals in reference revealed on autopsy pe- 
techiae in the kidneys, and in addition characteristic hemorrhage? 
(petechiae and ecchymoses) in one or more other organs. 

The animals that became infected were killed when severe 
symptoms developed in order that their blood might be used to 
hyper-immunize hogs in the routine of serum preparation. 



No. of expt in 

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Remarks on tabic No. 2, Section a. Experiment No. 1 was 
conducted in very hot weather. The material fed consisted of 
rind and subjacent fat. Portions were fed during a period of six 
days, and, especially in the later feedings, a decidedly rancid 
odor was present. It is possible that decomposition had something 
to do with the failure of such large quantities to produce infec- 
tion. The principal point to be noted is that most of the speci- 
mens fed produced hog cholera infection. 

Remarks on table No. 2, Section b. The experiments re- 
corded in this table were conducted to determine with what regu- 
larity fresh specimens from hogs killed while in the early stages 
of hog cholera, and the carcasses of which would pass inspection, 
would produce hog cholera when fed to susceptible pigs. Of the 
eight specimens fed, all produced the disease. 

Remarks on table No. 3, Section a. In this table, the meat 
referred to as frozen was hung in a rather open garret in an un- 
healed building from the time the animals were killed until sam- 
ples of their flesh were fed. The weather was such that the hams 
were frozen most of the time but in some cases there were perhaps 
a few days during which they thawed to some extent. The meat 
referred to as chilled was placed in an ordinary refrigerator dur- 
ing the time mentioned. 

It is very probable that experiment No. 17 would have proved 
negative had it been possible to obtain a subsequent check on the 
susceptibility of the pig fed. Litter mates of this animal were 
susceptible. Under the circumstances though the experiment was 
classed among those showing undetermined results. 

Experiments number twenty and twenty-two show interest- 
ing results. In Experiment No. 20 no visible symptoms appeared 
and no temperatures were taken. The pig subsequently proved to 
be immune in spite of the fact that it was a litter mate of seven 
others all of which were highly susceptible. Thus there is very 
little doubt that the animal was immunized by the material fed 
to it. Whether the immunizing effect was due to attenuation of 
the virus or to the small quantity of virus in the specimen is, of 
course, unknown. In Experiment No. 22 the pig fed showed moder- 
ate symptoms but recovered. At one time a temperature of 
106°F. was recorded. There is little doubt that it also was im- 
munized in the same manner. Further, it is highly probable that 
had it been one of a herd of susceptible pigs others would have 
been infected by associating with it. 





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Flesh and bone 
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In Experiment No. 21 the pig fed developed severe symp- 
toms and was killed in order that its blood might be used for virus. 
A careful autopsy revealed no lesions whatever so 2 c.c. of its 
blood were injected into a second pig. This pig developed symp- 
toms of hog cholera and showed on autopsy extensive hog cholera 
lesions so the experiment was classed among those producing posi- 
tive results. The original pig fed was simply one of those cases, 
'by no means uncommon, in which the disease actually exists but 
in which its presence cannot be verified by autopsy. 

Remarks on table 4. The cured hams from which the speci- 
mens were taken were prepared by a process known as sugar cur- 
ing. They remained in the brine approximately five weeks, and 
after being removed were smoked from seven to ten days in green 
hickory smoke. The brine was prepared according to the follow- 
ing formula : 

Common Salt 8 pounds 

Brown sugar 2 pounds 

Saltpetre 2 ounces 

Baking soda y 2 ounce 

Water " 4 gallons 

Dissolve all the ingredients in the water. Boil slowly for an hour 
and skim. Allow to cool before using. 

This has been selected as a representative formula for sugar 
curing. There are, of course, many formulae in use for this pur- 
pose but it is not likely that there is much difference in them as 
far as their effects on hog cholera virus is concerned. The only 
substances the use of which the federal regulations permit in preserv- 
ing meats are salt, sugar, various vinegars, pure spices, saltpeter and 
sodium nitrate. Benzoate of soda may also be used but its pres- 
ience must be declared on the label, and it cannot in accordance 
with the pure food law exist in finished food products in excess of 
3-10%. 

In sugar curing, vinegars are not used and benzoate of soda is 
used little if at all. Thus the only substances that might be used 
which do not appear in the above formula are sodium nitrate and 
pure spices. The former ingredient may be used to some extent 
in sugar curing processes, and of the spices, black pepper is quite 
frequently used. It is not likely though that sodium nitrate ex- 
erts more detrimental effects on virus than the corresponding 
potassium salt, and in the quantities in which they are used in 



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sugar curing it is doubtful if any of the spices operate to kill hog 
cholera virus. 

The outstanding fact -brought out in table number four is 
that the virus of hog cholera in pork is frequently but not always 
killed during the process of sugar curing. Just what makes the 
difference between those cases in which it is killed and those in 
which it is not killed? The three controllable factors involved in 
the destruction of viruses by chemicals are the kind of chemical 
used, its dilution, and the time during which it acts. Can any of 
these influences be so modified that they will destroy the virus in 
all cases? This is a question that still remains to be answered. 

As circumstances now appear there seem to be no chemicals 
that could well be substituted for salt and sugar as preservatives. 
The strength of the brine might be increased but there is a limit 
to an increase that would still leave the meat palatable. Increas- 
ing the time during which pork is in cure or increasing the time 
during which it is in the store house after being cured may offer 
•possibilities. The fact that the virus was killed in so many of the 
specimens might seem to indicate that the time limit during which 
it can survive the sugar curing process was being approached. 
As a matter of fact, however, there seems to be no definite relation 
between the time which the hams were in the store room and the 
certainty with which specimens from them would prove infec- 
tious. All the hams were in cure approximately six weeks. The 
■time during which different ones were in the store room varied 
from two to eighty-four days. Specimens from the hams repre- 
senting these two extremes did not prove infectious. On the 
other hand specimens from two hams in the store room fifty-seven 
and eighty days respectively were found to contain living hog 
cholera virus. It thus appears that if time is to foe employed as a 
factor in destroying hog cholera virus in sugar cured pork, store 
room cost and interest on money invested must be considerations. 

It will be observed that although rind was fed in large quan- 
tities in individual cases, no infection was caused by it. It was 
fed in only three experiments though, and so few negative results 
cannot have much significance. In one instance, ham No. 307, 
feeding the rind did not produce infection and flesh and bone and, 
also bone marrow washings from the same ham produced hog 
cholera. In this one instance the virus was evidently killed in the 
rind when it survived in the deeper parts. Since rind is very 



likely to find its way into garbage it is a matter of interest and 
importance to determine how frequently it carries hog cholera 
(virus, and it is to be regretted that during the time these experi- 
ments were in progress scarcity of susceptible pigs prevented de- 
terminations of this kind. They are not, though, essential. The 
real problem is not to determine whether there are parts of a ham 
that do not contain hog cholera virus; it is rather to determine 
whether there are parts that do contain it. Bone and bits of 
iclinging flesh are frequently placed in garbage and danger is al- 
ways present in case they contain virus. It is simply present in 
a greater degree in case it is found that rind also produces in- 
fection. 

Besides hams, the parts most frequently sugar cured are 
ishoulders and bacon. There are no good reasons to doubt that 
shoulders carry hog cholera virus in about the same proportion 
of cases that hams carry it. It seems quite probable that cured 
bacon, because of its thinness and because of the relative lack of 
vascularity of its parts, is less likely to contain virus than are 
ihams and shoulders. This is a point that must be determined 
with certainty before carcasses showing slight lesions only can be 
disposed of in the most economical manner. 

Viewing the entire situation from the standpoint of biology 
a very interesting group of co-related facts is encountered. If 
■the filterable virus were possessed of human intelligence it could 
iscarcely devise a more insidious and ingenious method of self 
preservation. It is known to multiply only in the bodies of swine 
and conditions favorable for its growth are therefore much re- 
istricted. Nevertheless, the difficulties met are overcome in a re- 
markable manner. The virus exists in the blood stream of the 
animals it infects and is thus distributed to all parts of the body ; 
at cannot at any time be detected with the microscope ; it is present 
an carcasses before gross examinations will detect it ; it does not 
infect human beings and thus escapes radical measures that would 
otherwise be taken for its destruction ; its presence in herds often 
drives them to market ; it secretes itself in pork where putrefaction, 
its most deadly natural enemy, is prevented or delayed by curing 
and low temperatures; then as a final link in a remarkable chain, 
the virus, in placing itself where possibilities for its distribution 
are practically limitless is at the same time placing itself in ma- 
terial which as a common practice is fed to hogs. 







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In general, the results shown in table No. 2, Section b„ should 
constantly be thought of in connection with those obtained in 
tables No. 3, Section a, and 4, Section a. The experiments re- 
corded in table No. 2, Section b, were conducted to determine 
whether hog cholera virus in sufficient quantities to infect swine 
is contained in hams taken from hogs killed while in the early 
stages of the disease. The experiments recorded in tables No. 3, 
(Section a) and 4, (Section a) were conducted to determine the 
effects of refrigeration and sugar curing on the life of hog cholera 
virus contained in hams. It seemed desirable in conducting the 
latter experiments to use hams from pigs known to be infected; 
otherwise it would not have been known whether negative results 
were due to absence of virus in the hams before they were treated, 
or to the fact that the virus was killed during the processes of re- 
frigeration and sugar curing. 

The experiments established two important facts; first, hog 
cholera virus in sufficient quantities to infect swine is quite con- 
stantly contained in fresh hams taken from hogs killed before 
symptoms, (other than rise in temperature) appear, and before 
lesions form; second, when specimens were taken from pigs show- 
ing lesions, 43% of the cured ones and 88% of the refrigerated 
ones proved infectious. 

Providing all originally contain virus in quantities sufficient 
to kill, there can, as far as we can see, be no conceivable difference 
between hams taken from pigs showing lesions and those taken 
from pigs that do not show lesions, as far as the effects of curing 
and refrigeration on the virus contained in them is concerned. 
However, in order to remove doubt concerning this point, experi- 
ments were conducted with two cured hams (table No. 4, Section 
b) and two refrigerated hams (table No. 3, Section b) taken from 
pigs showing no symptoms other than elevation of temperature 
and no lesions. One of the cured specimens and both of the re- 
frigerated ones produced infection. It therefore seems likely that 
had the hams referred to in table No. 2, Section b, been subjected 
to curing or refrigerating processes, the results would have been 
similar to those obtained from feeding specimens from virus pigs 
showing lesions. 

When the results of the experiments just described are ex- 
amined in their relation to practices observed in marketing, 
slaughtering, and inspecting swine, there are several phases of 
the situation that deserve consideration. 



Relative to marketing we are at once brought face to face 
with the fact that 40% of the pork consumed and 15% of that 
which is marketed in the country is not inspected. This is killed 
on farms, by local butchers, and by packing establishments that 
do not supply an inter-state trade. It is a well known fact that 
many herds are marketed as soon as hog cholera infection is dis- 
covered in them, and in places where there is no inspection prac- 
tically all hogs that appear well on foot are killed and sold for 
food. It is needless to add that large numbers of virus carrying 
carcasses must be included among those that reach our markets 
from these sources. Circumstances thus point to a need for ex- 
tension of both local and federal inspection. 

Turning now to the pork inspected under federal regulations 
let us examine the regulations themselves with a view to determin- 
ing how they operate to eliminate from the market carcasses that 
contain hog cholera virus. First, though, it should be stated that 
• the federal regulations compare favorably with those in force in 
other countries. The efficiency and thoroughness with which they 
fulfill their lawful purpose — the protection of human health and 
human life — is not questioned, but if they do not at the same time 
operate to protect the swine industry of the country, this fact. and 
the reasons for it should be known, the situation should be looked 
Bquarely in the face, and a remedy for it should be sought. 

Under existing conditions a consignment of cholera infected 
hogs reaches market and is first subjected to ante-mortem inspec- 
tion. With respect to hog cholera, it may contain five classes of 
hogs: first, dead hogs; these are condemned and tanked; second, 
hogs that show undoubted symptoms of cholera ; these are also 
condemned and tanked; third, hogs that show suspicious symptoms 
and temperatures below 106°F.; these are slaughtered; carcasses 
that show lesions of hog cholera are condemned or passed for 
pterilization according to the extent of the lesions; those that show 
no lesions are passed for food ; fourth, apparently normal hogs 
(and those showing suspicious symptoms) that have temperatures 
above 106 ; these are condemned or isolated for further tempera- 
ture records; in case further temperatures are taken the animals 
are condemned if their temperatures are still above 106° ; other- 
wise they fall into class three or class five; fifth, apparently nor- 
mal hogs that show temperatures below 106°F. ; these pass ante- 
mortem inspection and post-mortem as well if they do not show 



lesions of hog cholera in organs other than the kidneys or lymph 
glands. 

Briefly stated, the requirements in order that a given hog may 
pass inspection are that it shall not show undoubted symptoms of 
hog cholera, it shall not show suspicious symptoms plus any hog 
cholera lesions, it shall not show a temperature above 106°F., and 
regardless of ante-mortem findings the carcass shall not on post- 
mortem show hog cholera lesions in organs other than the kidneys 
or lymph glands. What are the chances for virus carrying car- 
casses to pass inspection? A consideration of symptoms, tempera- 
tures, and lesions in their relation to the time at which the flesh 
becomes infectious, will throw some light on this point. 

Relative to symptoms, it need only be stated that a hog will 
usually show elevation of temperature from one to three days be- 
fore any marked symptoms of hog cholera appear. The excite- 
ment to which hogs are subjected in shipping probably lengthens 
this time to some extent, because under such circumstances, a 
slight dullness and sometimes even graver symptoms cannot even 
by the closest scrutiny be detected. 

The temperature record, especially when the dividing point 
is placed as high as 106°F., offers a very uncertain standard upon 
which to separate infected animals from sound ones, but it consti- 
tutes a most valuable adjunct to other factors employed for the 
purpose. In the first place there is a wide variation in the normal 
temperatures of swine — from 101°F. to 104°F. In the second 
place weather conditions, excitement due to shipping, and other 
factors that cannot be controlled alter otherwise normal tempera- 
tures very materially. It is very probable that most of these in- 
fluences when they affect temperatures noticeably, operate to ele- 
vate rather than to lower them, and this probably is the reason 
why the dividing point — 106 °F. — has been placed so high. It is 
certain that some hogs may carry temperatures near 106° as a re- 
sult of excitement or exertion, and it is equally as certain that many 
others carry temperatures below 106° when they are suffering with 
hog cholera. 

Another important thing to recognize is the usual hog cholera 
curve. It rises quite rapidly as a rule, remains high for a few 
days, and then takes a decided drop, which, if death does not en- 
sue, is followed by a second elevation. The following, reproduced 
from Hutyra and Marek is intended to show a typical hog cholera 



curve. It appears originally in the centigrade scale, but it lias for 
the sake of convenience been changed to Fahrenheit. 

The temperature curves we record in young pigs usually rise 
above 106° for a short time, and as a rule they do not fall quite as 
low between the first and second elevations as did the above curve 
(Jan. 21). In other ways the curves we record correspond quite 



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closely to the one shown. In this particular case the animal in 
question would not, except during the very latest stages of the dis- 
ease, have been condemned on account of its temperature: symp- 
toms were not recorded until three days after the first decided ele- 
vation of temperature occurred; unless the animal was an excep- 
tion, lesions sufficient to condemn it had not formed during the first 
day or two on which high temperatures were recorded- Thus there 



was probably a day or two during which its blood was infectious, 
when it would have passed inspection. 

In order to show more fully something of the number of hogs 
that will not be rejected on account of high temperatures the fol- 
lowing curve, prepared by Craig and Whiting, is reproduced. 
The animals were infected with intra-muscular injections of small 
quantities of hog cholera virus. There were 250 of them and the 
curve shows their average daily temperature during the course of 
the disease. A second curve, prepared by the same authors, shows 
the average daily temperature of twenty hogs exposed to cholera 
by means of natural infection. 

It will be understood that on any given day many of the tem- 
peratures were above and many were below the point indicated. 
It should also be remembered that there was a period during the 
time when the curve was ascending when a large number of normal 
temperatures were averaged with a few that were above normal. 
In this respect the curves are slightly misleading but taken as a 
whole they indicate that during the course of the disease most of 
the animals showed temperatures below 106° most of the time. 

When the lesions are considered as a factor in determining 
which carcasses shall be condemned it is to be remembered first of 
all that in some cases, even when hogs are allowed to die of cholera, 
lesions do not form at all. Carcasses representing this class to- 
gether with those that do not show lesions in organs other than 
the kidneys and lymph glands are allowed to pass. Hogs do not 
as a rule show marked lesions during the first day or two that ele- 
vated temperatures are recorded, and often the time between the 
first rise in temperature and the time when lesions sufficient to 
condemn are formed, is of much greater duration. Exemption of 
the kidneys and lymph glands from consideration unless there are 
lesions in other organs sufficiently well marked to cause carcasses 
to be sent to the retaining room, undoubtedly results in passing 
many virus carrying carcasses. 

When table No. 2, is examined in its relation to the symptoms, 
temperature, and lesions necessary to condemn an animal or car- 
cass for hog cholera, we cannot well escape the conclusion that 
there is a time in the life of nearly every hog infected with acute 
hog cholera when it will pass inspection and when bits of pork 
from its carcass will prove infectious if fed to other swine. This 
time varies from a few hours to several days and is measured, 



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roughly, by the time required for the temperature to rise from nor- 
mal to 106°, or by the time required for symptoms to develop or 
extensive lesions to form after the temperature curve starts up- 
ward. It is possible that the meat of some hogs is infectious even 
before the rise in temperature takes place, for it is to be remembered 
that hog cholera vims causes the elevation and it must therefore be 
present before the elevation occurs. Whether, or for how long, it 
is present in quantities sufficient to infect, and before the elevation 
of temperature occurs, are questions on which we have insufficient 
data. 

Considering again the infected herd as it is unloaded from the 
car and comparing it with similar herds in the field in which ob- 
servations have been made and temperatures have been taken, we 
cannot help knowing that there are often present in such herds con- 
siderable numbers of apparently healthy hogs that show high tem- 
peratures due to hog cholera. Some of these are weeded out on 
account of temperatures above 106°, and a few on account of 
lesions, but many cannot do otherwise than pass. How many, we 
do not know, but for purposes of comparison it may be stated that 
during the decade ending in 1911 a yearly average of 18000 hogs 
were condemned because of cholera. 

Each infected carcass passed possessed almost infinite possi- 
bilities in regard to its final distribution. Parts may be worked 
up into sausage or cooked products and hams, shoulders, and bacon 
may be cured or shipped in fresh or refrigerated form to supply 
retail butchers. These facts, coupled with what our experiments 
have shown relative to the probabilities for the presence of hog 
cholera virus in market pork, readily lead to the belief that what- 
ever may be the means of spreading hog cholera from herd to herd 
in different localities, its spread from locality to locality could, if 
all facts were known, be traced in many cases to shipping and 
slaughtering hogs in the early stages of cholera and the subsequent 
sale of pork from the carcasses of these animals. 

The results of the experiments described suggest the need of 
preventive measures for the purpose of diminishing the number of 
infections due to feeding pork trimmings. These measures natur- 
ally fall into three general classes: .first, measures to prevent 
marketing cholera infected hogs; second, measures to turn more 
carcasses from infected herds into products in which the virus will 
be killed; third, measures to acquaint swine breeders with the 



danger involved in feeding garbage containing pork trimmings, 
and with the ways to avoid this danger. 

Preventing the shipment of cholera infected herds should be 
the first object sought because it attacks the trouble at its source. 
There will be widespread infection as long as this is a common prac- 
tice, and it will 'be a common practice so long as it is possible to 
sell infected hogs for the price that sound ones bring. Since the 
discovery of anti-hog cholera serum the breeder has in it an agent 
which at any given time will usually protect all of his hogs which 
are not, at that time, already dangerous carriers of the hog cholera 
virus. This statement is based on the facts that pork from hogs 
killed as soon as an elevation of temperature is recorded proves to 
be quite generally infectious, and that serum will usually protect 
hogs treated before an elevation of temperature takes place. Thus 
it is true that the enactment and enforcement of measures to pre- 
vent shipping cholera infected herds need not cause undue hard- 
ships in any place where hog cholera serum is available. 

The economic difficulties involved in condemning or passing 
for sterilization infected carcasses which, in reality, are entirely 
fit for human food, are of a nature which render them very diffi- 
cult to overcome. The scientific difficulties met in seeking to re- 
move all carcasses that contain virus are no less trying. It has 
been shown that the carcasses of hogs that show no symptoms other 
than slight elevation of temperature, and no lesions whatever, 
may contain hog cholera virus sufficient to infect other hogs. Be- 
cause the normal temperatures of swine vary so widely no mark 
can be set that will separate out infected animals with any degree 
of accuracy. A temperature of 104°, for instance, may be normal 
or three degrees above normal. There is no method known of de- 
tecting all virus carrying carcasses, but, as a general principle, 
we believe that rigid ante-mortem herd inspection with a more se- 
vere interpretation of temperatures and lesions in hogs that are 
members of infected herds, together with a tagging system ren- 
dering it possible to place losses due to condemnation with the man 
who ships the hogs, are worthy of consideration. Obviously meas- 
ures of this kind would serve the double purpose of removing more 
infected carcasses from sale in the form of raw products, and of 
preventing the shipment of many infected herds that otherwise 
reach our markets. 

Under existing conditions the most promising outlook for 



dealing with Hi is phase of hog cholera control consists in acquaint- 
ing swine breeders with the dangers incident to feeding their own 
kitchen refuse, in case there are trimmings from market pork con- 
tained in it. The ordinary farmer has recourse to four very ef- 
fective methods of protecting his herd from dangers incident to 
ga'rbage feeding ; he may keep pork trimmings out of the garbage, 
he may discontinue the practice of feeding garbage, he may cook 
all garbage before it is fed, or he may immunize his hogs. Men 
who collect and feed kitchen refuse from cities have recourse only 
to the two last named methods of protection. 

It is sometimes suggested that statutory restrictions should be 
placed on feeding collected garbage to hogs. The objections to 
this practice are that it is in a degree repulsive, and that the heavy 
losses caused by it more than offset the gain it produces. The first 
objection is well sustained in many individual cases and in others 
it is not. The French have a saying, "Not what, but how", and 
this applies well to the point in question. If the material is fed 
fairly fresh and if the hogs to which it is fed are provided with 
clean quarters there are no very well sustained objections to the 
practice, for the material fed is in the last analysis only the refuse 
from what we ourselves eat. Many thousand hogs are fattened on 
garbage each year and statutory restrictions placed on the prac- 
tice as a whole would not, especially since the discovery of anti-hog 
cholera serum, be justified. 

Cooking kitchen refuse to destroy hog cholera virus contained 
in it is very effective in individual cases, and it possesses the addi- 
tional advantage of rendering much of the material in it, — for in- 
stance potato parings, — more palatable and more nutritious. It 
could not, though, be well enforced as a sanitary measure; it is 
quite expensive in some localities, and, in order to be effective it 
requires more time and care than most men will give to it. 

Serum-virus immunization seems to be the most logical means 
of preventing hog cholera in large herds that are fed collected gar- 
bage. It is effective, reasonably cheap, and has the decided ad- 
vantage of protecting from infection by channels other than the 
one incident to feeding kitchen refuse. 

Summary and Conclusions 

1. Meat and bone taken from the carcasses of hogs killed be- 
fore any manifestations of hog cholera other than elevation of tern- 



perature take place, and at a time when they will pass inspection, 
will usually produce hog cholera when fed in small quantities to 
susceptible pigs. 

2. In places where meat inspection is maintained, it is im- 
possible, even with the severest interpretation of temperatures, 
symptoms and lesions now practicable, to remove from market all 
carcasses of hogs that contain hog cholera virus. 

3. We believe a more severe interpretation of temperatures 
and lesions in hogs known to come from infected herds, will re- 
move many more virus containing carcasses than are now removed, 
and without resulting in the condemnation of appreciable numbers 
of carcasses that do not contain virus. 

4. The economic difficulties in the way of placing more severe 
interpretations on temperatures and lesions observed in hogs that 
are members of infected herds are worthy of study. Whether the 
number of virus carrying carcasses that pass inspection is large or 
small, the danger of new infections due to passing them is pro- 
portionate to the number passed. 

5. In hog cholera infected carcasses that pass inspection : 
The virus is not often killed in parts sold as fresh or refriger- 
ated products. 

The virus is often, but not always, killed in hams that are 
sugar cured. (In our experiments in twelve cases in twenty-one). 

6. Anti-hog cholera serum will, at any given time, usually 
save all hogs in a herd the carcasses of which will not at that time, 
already prove infectious if small parts are fed to susceptible pigs. 

7. Measures to prevent hog cholera infections due to feeding 
trimmings from market pork should include efforts to prevent mar- 
keting infected herds, efforts to prevent the sale of carcasses in pro- 
ducts in which the virus is not killed, and efforts to acquaint swine 
breeders with the danger incident to feeding kitchen refuse. 

8. Farmers can avoid the danger mentioned by discontinu- 
ing the feeding of kitchen refuse, by placing all pork trimmings 
elsewhere than in the garbage pail, by thoroughly cooking all 
garbage before it is fed, or by immunizing their hogs. Men who 
collect and feed city garbage can avoid the danger by cooking all 
the material they feed, or by immunizing their hogs. 

Acknowledgement. The writer is deeply indebted to Dr. 
V. A. Moore whose keen interest in the work has been a constant 
source of encouragement, and whose advice has been frequently 



soughl and utilized during the four years iu which the experi- 
ments were in progress. 

EEFERENCES 

1. King. Bulletin No. 71, Kansas Experiment Station. 

2. Law. Veterinary Medicine. 

3. EUTYRA am) MAREKs Pathology and Therapeutics of the Diseases of Do- 
mestic. Animals. 

I. Friedburger and Fkohner. Special Pathology and Therapy of Domestic 
Animals. 

5. DORSET. Hog Cholera Control Investigations of the U. S. Dept. of Agri- 
culture. Report of the eighteenth annual meeting of the V. S. Livestock 
Sanitary Association. (Report of progress). 

6. MrCiiAKAV. Hog Cholera. Proceedings of the American Veterinary Medi- 
cal Association, 1912. 

7. Birch. A Study of Hog Cholera Transmission. Cornell Veterinarian, 

October, 1914. 



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